Erki,
The millisec site says the FOP32 is the replacement for the FKP32 and is designed to also work on the Duron/T-bird, so no real difference in cooling. The FDP32 is a real good unit but BIG.
They give the dimensions so check to make sure they will fit on your board. I have some capacitors right against the cpu so had to be careful the heatsink would clear them.
The FKP and FOP have the fins raised up some so they will clear the capacitors.
I would measure carefully how much free area you have and if capacitors are close, how high they are. Then if you have a question about fit, just e-mail the place your buying from and ask them if they think it will fit.
You can check out the cooling reviews at Reviewclick, they have reviews for both the FKP and FDP, FOP is new so no reviews yet.
Any one of these will be a BIG improvement and you should be able to close the case up again.